The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Methods of measuring a sample are desirable. For example, it is desirable to be able to measure the geometry of features on a sample with resolution on the order of micrometers or nanometers, for instance in the case of semiconductor integrated circuits and photomasks, microelectromechanical devices, and other microstructures. Additionally, surface and subsurface objects, defects, and anomalies in a sample or device may result in detrimental effects when the device is used. As an example, it is desirable to be able to detect unwanted contamination particles present on photoreticles (and their protective pellicles) used in the mass production of integrated circuits as well as the detection of other defects that might arise during fabrication of these integrated circuits. Other examples of the usefulness of measuring samples in the integrated circuit industry include the evaluation of buried conductor traces in multiple insulating layers and the characterization/imaging of high aspect ratio isolation trenches that prevent current leakage between adjacent integrated circuit (IC) components. Additionally, it may be desirable to measure magnetic and electric field patterns created in the vicinity of operating integrated circuits.
In the early 1980's Binnig and Rohrer developed the scanning tunneling microscope (STM). In this same year, Binnig, Quate, and Gerber invented the atomic force microscope (AFM), which is built on the principles of the STM. In general, an AFM works by monitoring forces between a sharp probe tip and a sample as it is precision scanned over the surface of the sample. In 1984, Matey and Blanc of RCA Laboratories invented scanning capacitive microscopy (SCM) where they utilized pre-developed instrumentation and pickup circuitry from the RCA capacitive electronic disc (CED) VideoDisc player. SCM is similar to AFM but specifically targets changes in capacitance between the probe tip and the surface, and for this reason, SCM is also referred to as scanning probe capacitance imaging. These inventions in the 1980's have spawned a great deal of research into the use of scanning probe microscopy as a means for high-resolution imaging of objects at both macroscopic and microscopic scales.
In the most general sense, an SCM works by scanning an electrically conducting probe over the surface of a sample. FIG. 1, which is taken from Applied Physics, by J. R. Matey and J. Blanc, Volume 57, page 1437 (1985), illustrates the basic geometry of a prior art SCM probe head 10 over a sample 14. As shown by FIG. 1, the SCM probe head 10 houses a sharp tip electrode 12, which is scanned over the surface of the sample 14.
An image is created by monitoring local changes in capacitance between the sharp tip electrode 12 and the sample 14 or a conducting surface under the sample 14. This change in capacitance serves as the contrast agent in the generated image. While there have been many different approaches toward improving SCM, primarily with respect to probe shape, pickup circuitry, and image reconstruction, what has remained common amongst groups attempting to develop high-resolution nanometer scale imaging devices via AFM SCM is the use of a single sense electrode. A well-known and well-documented pitfall of the single sense electrode is its inherent lack of ability to shape the electric field to a desired configuration in order to allow selective spatial imaging. While it is possible to raster scan a single probe electrode over a surface with high lateral resolution, such a configuration does not, for example, provide information for characterizing the depth and volume of the sample in desired spatial dimensions. Consequently, the single probe design cannot optimize spatial and depth parameters and resolution, such as depth and width A single probe also does not allow high imaging speed of the area of a surface to be measured.
Magnetic scanning probe microscopes are another technology, analogous to SCM and used to image magnetic properties. Other magnetic sensors are used in the industry to detect fine patterns. For example, the magnetic read head on a hard disk is used to detect very fine magnetic bit patterns on the surface of a hard disk platter. However, arrays of magnetically driven and/or detected sensors have not been used to generate high resolution two-dimensional and three-dimensional images of submicron scale.
Electromagnetic electrode arrays (electroquasistatic, magnetoquasistatic, and electrodynamic) for object detection and mapping have been used in widely different fields implementing various different electrode geometries. Examples include the use of circular electrode rings for the mapping of biological systems inside the ring (commonly referred to as electrical impedance tomography (EIT)), and the use of coplanar, interdigital electrodes for buried object detection and non-destructive testing. Unfortunately, electroquasistatic electrode arrays and magnetoquasistatic coil arrays have not yet been utilized to generate high resolution, two-dimensional and three-dimensional images of sub-micron scale devices, such as, for example, integrated circuit features.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.